Mt Tongariro at sunset after the eruption, seen from a lookout point on Te Ponanga Saddle Rd.

Groups of Auckland school students will continue to visit Mt Tongariro today but will stay away from the areas affected by yesterday's eruption.

An eruption at Te Maari crater, on the mountain's north-west side, about 1.30pm, sent a 2km-high ash plume into the sky causing panic and excitement for nearby trampers, including groups of children on camp.

Scientists have since warned further eruptions at Mt Tongariro may continue for months, if not years.

A group of 20 students and 10 adults from Gulf Harbour School were on the mountain when it erupted, and students from St Kentigern College has just arrived in the area. Further groups from St Kentigern College are due to arrive today and tomorrow.

Principal Steve Cole sent a newsletter to parents to ensure their children were "safe and well" and advised their trip would continue.

He said the Tongariro Crossing track was closed but everything else in the area was "operational and safe".

Advertisement

"Our programme will be directed away from the [crossing] area.

"Please be reassured that we will be taking the safety of all attending Field Centre 2012 very seriously and should the situation change we will advise families as soon as practical," the letter said.

Teacher Lomi Schaumkel from Tamatea Intermediate in Napier yesterday told how his group was near the Katetahi hot springs when the eruption began.

''We were right up there next to it. It was just amazing. It was pretty scary from where we were and it just looked absolutely spectacular, the ash that came out. It really did look like one of those atom bomb explosions, and it made a rumbling sound," he said.

There were 90 students, six parents and four teachers in the group.

"Some panicked, some didn't. Everyone came down safely and it was great."

Yesterday's eruption was the second this year, after Tongariro erupted in August - the first time in more than 100 years.

Vulcanologists only had those historical events to compare the recent activity to, and said that a series of eruptions in the late 1800s indicated that more eruptions were to follow.

"We cannot say what will happen next at Tongariro but the scenario considered most likely, based on the August 2012 eruption and the description of late 1890s eruptions, is that we could expect another eruption of similar size at any time during the next few weeks," GNS vulcanologist Brad Scott said.

Known eruptions at Tongariro occurred in 1869 and intermittently in the years between 1886 and 1897.

Research based on volcanic events around the world showed that eruptions usually came in a series, Scott said.

"When you get an eruption it can stop, but most of the time there's further eruptions over months or years."

Any further eruptions at Tongariro, however, were not expected to escalate in size.